Catalysis and Catalytic Reactors Questions and Answers

Answer: A

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: the very fine particles used in a slurry give short diffusion paths and effectiveness factors near unity, and filtering that fine solid out of the product is one of the process’s real difficulties. Statement 3 is wrong - a slurry reactor holds catalyst suspended in a *liquid*, and is used for three-phase reactions such as hydrogenations, with the gas sparged through.

Answer: B

Smaller particles help the chemistry and hurt the hydraulics, so the size is a compromise. Shaped catalysts such as rings and trilobes are made to improve the trade-off between the two. Particle size is always a compromise.

Answer: C

Both are true and the reason gives the design objective, and it is a good example of a geometric solution to a conflict between two physical requirements. Void fraction rises with the shaped forms. Geometry solves a conflict the chemistry cannot.

Answer: D

Two half lives leave a quarter of the original activity. Catalyst life is usually described this way and sets the interval between charges or regenerations. First order decay halves it each period. Two half lives leave a quarter behind.

Answer: A

The extra rate compensates for the lost activity and holds conversion steady, and the end of run temperature is what limits the cycle. Raising it too far accelerates sintering and coking further. End of run temperature limits the cycle.

Answer: B

The straight channels let the exhaust pass with little resistance, which matters greatly to engine performance. Its surface area per unit volume is lower than a packed bed and it is not cheap. Back pressure is the overriding constraint.

Answer: C

Both are true and the reason gives the priority: a packed bed of the same activity would restrict the exhaust unacceptably, so the geometry is chosen for the hydraulics rather than the chemistry. Straight channels give a clear path.